Aluminum base alloy article



known as recrystalii' 'ttion, i.

ALUMINUMBASEALLQY ARTICLE William A. Anderson, Verona, Pa., assignor toAluminum Company of America, Pittsburgh, Pa., a corporation ofPennsylvania No Drawing. Application July 9, 1953 ,SerialNo. 367,096

7 Claims. (Cl. 148-32) This invention relates to aluminum base alloyarticles which have unique softening characteristics in response toannealing.

As is well known, aluminum in common with many other metals becomesharder and stronger at the expense of ductility when it is rolled,pressed, or otherwise deformed within a temperature range that does notpermit the formation of new grains. it is also well recognized that thestrain created by such deformation can be relieved by heating the workedproduct to a temperature between 640 and 670 F. Such a thermal treatmentis commonly referred to as annealing and the change brought about in theinternal structure of the metal is e., the formation of new crystalsfrom the fragments created-by the deformation. The occurrence ofrecrystallization, as recognized by'those skilled in the art, isdetected by microscopic ex amination of a properly etched specimen andobserving whether new grains or crystalshave been formed from the grainfragments. The presence of new grains in substantial numbers may also bedetected by the X ray diffrac tion method. Further, a marked change instrength and elongation accompanies the formation of new grains. Tensiletests to determine these properties therefore provide a practical andrapid means of learning wether recrystallization has taken place.Although recrystallization. of aluminum occurs Within the foregoingtempera -ture range it is possible to obtain this result at a lowertemperature depending upon the duration of the treatment, the purity ofthe metal and the extent to which the metal has been deformed or coldworked. The

obtaining non-uniform results, and the attendant increase 1 in cost.

As has been mentioned above, the purity of aluminum influences itstemperature of recrystallization. For example, metal of a purity of99.998% has been reported to recrystallize atg2l2 F. within aperiod of 6to 10 minutes following a reduction in thickness of about 91% by coldrolling. The commercial exploitation of such super purity metal is ofcourse limited by its cost and the amount which is available. Hence,even if such high purity metal were otherwise satisfactory, it would notbe a competitor of *low purity material when large quantities arerequired. Also, the advantage of a low recrystallization temperaturefound in high purity metal is lost as the impurity content reaches thelevel found in metal of ordinary purity.

Although a low recrystallization temperature is of small importance insome cases, in others it may the "ice determining factor. An example ofthis is found in the sheathing of insulated telephone cable. Accordingto one process of making such sheathed cable a cold worked aluminum tubeis drawn down upon the core of insulated wires. However, in order toprovide the necessary ductility in the aluminum sheath the whole cablemust be subjected to an annealing operation. A conventional annealingtreatment cannot be employed for this purpose because it would destroyor greatly injure the insulation on the wires comprising the cable. ittherefore becomes necessary to employ a sheathing which can be softenedand made more ductile without damage to the insulation.

.It is an object of this invention to provide a wrought aluminum alloyarticle that has a lower recrystallization temperature than aluminumcontaining the same impurities in the same amounts as the alloy. Anotherobject is to provide a wrought aluminum alloy article whichrecrystallizes at a faster rate than aluminum con taining the sameimpurities in the same amount under the same conditions of work andthermal treatment. A further object is to provide a means for loweringthe recrystallization temperature of cold worked aluminum alloy articlescontaining up to 0.8% total of iron and silicon impurities. Anotherobject is to utilize aluminum of a purity commonly produced to formalloy articles having a lower recrystallization temperature than thealuminum without the alloy addition. Still another ob ject is to providean aluminum cable sheathing which can be annealed without damage to theinsulation.

I have discovered that a lower recrystallization temperature and ahigher rate of recrystallization can be obtained in a wrought aiuminousarticle by forming the article of an aluminum alloy consistingessentially :of

aluminum, at least 0.01% each of iron and silicon, the total ofthetwoelements not exceeding 0.8%, the amount of iron not exceeding theproportion of 4 parts of iron to 3 parts of silicon, a maximum of 0.05%each of copper and magnesium as impurities, 0.005 to 0.25% berylliumwand0.04 to 1.0% nickel than by using aluminum containing the sameimpurities in the same quantity, and worked to the same extent but withno beryllium and nickel addition. By observing the foregoing iron andsilicon ratio together with making the beryllium and nickel additions ithas been possible to obtain a recrystallization temperature in a coldworked article which is as much as 200 F. lower than that of aluminum ofthe same purity without the addition of beryllium and nickel and whichhas received the same amount of cold work.

To state the matter differently, the cold workedaluminum-beryllium-nickel alloy product can be annealed at a lowertemperature or in a shorter time at a higher temperature than the samearticle made of aluminum containing the same kind and amount ofimpurities as those occurring in the alloy. Moreover, the results ofannealingthe cold worked alloy articles have been found to be uniformwhich is of considerable importance from the standpoint of manufacturingoperations.

Control of the iron and silicon impurities within the specified limitsis essential to the production of a wrought article having the lowrecrystallization characteristic. While the minimum amount of iron andsilicon should be 0.01% of each, the total should not exceed 0.8% of theweight of the alloy and preferably the total amount should be within therange of 0.1 to 0.5%. In an alloy having less than 0.01% each of ironand silicon nothing is gained by adding beryllium and nickel as far asreducing the recrystallization temperature is concerned. 0n the otherhand, if more than a total of 0.8% of these impurities is present, theberyllium and nickel additions have no substantial effect on thetemperature of recrystallization. To secure the best result the minimumamount of iron and silicon should be 0.03% of each. Within the foregoingranges for iron and silicon, the iron content should not be more than ofthe silicon content and to obtain the best results it should not exceedof the amount of silicon. In the latter case, the minimum amount ofsilicon would be proportionately higher than 0.01% and in preferredpractice the minimum iron content should be 0.03% while the lowestsilicon content should be 0.04%. Unless the ratio of iron to silicon isobserved the benefit from the beryllium and nickel addit ons is greatlyreduced.

In regard to other impurities any copper and magnesium should be kept ata minimum, the maximum amount of each not exceeding 0.05 as mentionedabove. Still other impurities, such as manganese, titanium, zirconium,molybdenum, chromium and vanadium may be present but in very smallamounts, usually less than 0.01% each, and the total should not exceed0.02%. In these amounts they do not offset the beneficial effect ofberyllium and nickel upon the recrystallization temperature.

The addition of 0.005 to 0.25% beryllium and 0.04 to 1.0% nickel toaluminum of the purity defined above and having the proper ratio of ironto silicon has the surprising effect of producing an alloy having alower temperature of recrystallization and a higher rate ofrecrystallization when used in the form of a worked article thanprevails in the absence of beryllium and nickel. Although the individualaddition of beryllium or nickel to aluminum lowers t..erecrystallization temperature, as described and claimed in myctr-pending applications Serial Nos. 367; 094 and 367,095, respectively,I have found that an even greater eiiect is produced by the simultaneoususe of these elements. The effect is greater than would be expected fromthe sum of the individual elements.

The addition of alloying elements to aluminum has always been found toraise the recrystallization temperature and hence the discovery of theopposite effect of beryllium and nickel is indeed surprising. Noexplanation of this result is offered. To obtain the optimum benefitfrom the additions of 0.01 to 0.1% beryllium and 0.15 to 0.5% nickelshould be used, especially where the iron impurity is less than A of thesilicon content. The beryllium and nickel additions can be made in anyone of the conventional ways of introducing the metals.

As stated above, the amount of cold work influences the temperature atwhich recrystallization will occur. In order to obtain the lowestrecrystallization temperature, the alloy articles should receive areduction in thickness of not less than 20% or be given an equivalentminimum amount of cold work. A reduction in thickness of at least 40% oran equivalent amount of cold work is usually desired While reductions orcold work exceeding 90% are preferred. Such reductions are not difficultto obtain in commercial practice for the alloy is easily fabricated,

and in some instances no intermediate annealing may be required inproducing the final shape from an ingot.

One of the advantages of my invention rests in the increase in rate ofrecrystallization which can be obtained at temperatures where aluminumwithout beryllium and nickel is annealed. Thus, if one does not wish totake advantage of the lowest possible annealing temperature permitted bythe addition of beryllium and nickel, a higher temperature can be usedand obtain a considerable reduction in the length of time required toeffect complete recrystallization. It is well known in annealingaluminum, for example, that with but slight cold working a very longperiod of time may be required to bring about completerecrystallization. Also, even where the cold working is severe the rateof recrystallization may be low if the annealing temperature is veryclose to the temperature of recrystallization. Under either conditionthe ad dition of beryllium and nickel and control of the ratio of ironto sil con will accelerate recrystallization. For example, it has beenfound that with an aluminum alloy sheet composed of aluminum, .0l6%beryllium, 0.18% nickel, 0.03% iron and 0.04% silicon, which had beencold rolled 90% and annealed at a temperature of 400 B, it was possibleto obtain complete recrystallization within a period of 15 minutes,whereas, aluminum sheet of the same purity and with the same amount ofcold work must be heated at 600 F. to produce complete recrystallizationin the same length of time.

The rate of recrystallization is determined by noting when new grainsfirst form and the time elapsed until substantially all of the grainfragments have formed new grains. Such. a determination is mostconveniently carried out by testing a series of samples cut from thesame sheet or other article, heating them to a given temperature andremoving the samples at specified time intervals and observing theextent to which recrystallization has occurred. Although the presence ofnew grains can be microscopically detected upon a proper etching of themetal, it is advisable to supplement the examination with an X-raydetermination.

The eilect of beryllium and nickel upon the recrystallizationtemperature of cold rolled sheets of the alloy, especially the combinedeifect of these elements, is illus trated in the following examples.

Aluminum of 99.9% purity containing 0.03% iron and 0.04% silicon wasemployed as the base melt. Nine melts of this metal were prepared anddiflerent amounts of beryllium and nickel added to each melt except theone serving as the blank or control sample. The alloyed and non-alloyedmelts were cast and the ingots rolled to 0.050" thick sheet so that thefinal product had a reduction in thickness of 90% after the intermediateanneal. Samples of sheet of each composition were heated to and held ata selected temperature for /2 hour. The beryllium and nickel contents ofthe sheet samples and the lowest temperatures at which recrystallizationwas complete appear in the table below.

Recrystallization temperatures of Al-Be, Al-Ni and Al-Be-Ni alloysRecrystal- Percent Be or Ni lization Temperature, F.

0 600 0.017 B 475 0.20 N i 500 0.19 Ni+0.007 Be" 450 0.18 Ni+0.012 Be"400 0.17 Ni+0.022 Be 400 0.30 Ni+0.015 Be 400 0.41 Ni+0.0l5 Be 400 Oneof the applications for the aluminum-beryllium product made inaccordance with my invention is that of forming a sheath for insulatedpower and telephone cable. As has been mentioned, the sheathing of suchcable has presented a diflicult problem because of the necessity forsoftening the sheath after it has been drawn down upon the insulatedwires. It has been found that the aluminum-beryllium-nickel product, asdefined above, provides a very satisfactory sheath from the standpointsof application to the cable, of being annealed on the cable, and theflexibility of the final cable product. Such advantages, it can bereadily appreciated, are of particular importance in providing aseamless sheath on a cable. 7

This application is a continuation-in-part of my copending applicationSerial No. 172,003, filed July 3, 1950.

Having thus described my invention and certain embodiments thereof, Iclaim:

1. An aluminum base alloy article which has received at least 20% coldwork, said alloy consisting of 0.005 to 0.25% beryllium, 0.04 to 1.0%nickel, a maximum of 0.05% each of copper and magnesium impurities, at

least 0.01% each of iron and silicon, the total quantity of iron andsilicon not exceeding 0.8% and the amount of iron not exceeding 9 of thesilicon content, and the balance aluminum except for other impuritiesthan those named hereinbefore, said cold worked alloy article beingcharacterized by a lower temperature of recrystallization when annealedthan aluminum containing only impurities including not less than 0.01%each of iron and silicon and not more than a total of 0.8% of iron andsilicon, but the ratio of said iron to silicon exceeding 4 to 3, wheresaid aluminum has received the same amount of cold work as said coldworked article.

2. An aluminum base alloy article which has received at least cold work,said alloy consisting of 0.005% to 0.25% beryllium, 0.04 to 1.0% nickel,a maximum of 0.05 each of copper and magnesium impurities, at least0.01% each of iron and silicon, the total quantity of iron and siliconnot exceeding 0.8% and the amount of iron not exceeding of the siliconcontent, and the balance aluminum except for other impurities than thosenamed hereinbefore, said cold worked alloy article being characterizedby a lower temperature of recrystallization when annealed than aluminumcontaining only impurities including not less than 0.01% each of ironand silicon and not more than a total of 0.8% of iron and silicon, butthe ratio of said iron to silicon exceeding 3 to 4, where said aluminumhas received the same amount of cold Work as said cold worked article.

3. An aluminum base alloy article which has received at least 20% coldwork, said alloy consisting of 0.01 to 0.1% beryllium, 0.15 to 0.5%nickel, a maximum of 0.05% each of copper and magnesium impurities, atleast 0.03% of iron and 0.04% of silicon, the total quantity of iron andsilicon not exceeding 0.5 and the amount of iron not exceeding of thesilicon content, and the balance aluminum except for other impuritiesthan those named hereinbefore, said cold worked alloy article beingcharacterized by a lower temperature of recrystallization when annealedthan aluminum containing only impurities including not less than 0.01%each of iron and silicon and not more than a total of 0.8% of iron andsilicon, but the ratio of said iron to silicon exceeding 3 to 4, wheresaid aluminum has received the same amount of cold work as said coldworked article.

4. An aluminum base alloy article which has received at least 40% coldwork, said alloy consisting of 0.005 to 0.25% beryllium, 0.04 to 1.0%nickel, a maximum of 0.05% each of copper and magnesium impurities, atleast 0.01% each of iron and silicon, the total quantity of iron andsilicon not exceeding 0.8% and the amount of iron not exceeding 44), ofthe silicon content, and the balance aluminum except for otherimpurities than those named hereinbefore, said cold worked alloy articlebeing characterized by a lower temperature of recrystallization whenannealed than aluminum containing only impurities including not lessthan 0.01% each of iron and silicon and not more than a total of 0.8% ofiron and silicon, but the ratio of said iron to silicon exceeding 4 to3, where said aluminum has received the same amount of cold work as saidcold worked article.

5. An aluminum base alloy article which has received at least 90% coldwork, said alloy consisting of 0.01% to 0.1% beryllium, 0.15 to 0.5%nickel, a maximum of 0.05 each of copper and magnesium impurities, atleast 0.03% of iron and 0.04% of silicon, the total quantity of iron andsilicon not exceeding 0.5 and the amount of iron not exceeding of thesilicon content, and the balance aluminum except for other impuritiesthan those named hereinbefore, said cold worked alloy article beingcharacterized by a lower temperature of recrystallization when annealedthan aluminum containing only impurities including at least 0.03% ironand 0.04% silicon and not more than a total of 0.5% of iron and silicon,but the ratio of said iron to silicon exceeding 3 to 4, Where saidaluminum has received the same amount of cold work as said cold workedarticle.

6. An annealed aluminum base alloy cable sheath which prior to annealingreceived at least 20% cold work, said alloy consisting of 0.005 to 0.25%beryllium, 0.04 to 1.0% nickel, a maximum of 0.05 each of copper andmagnesium impurities, at least 0.01% each of iron and silicon, the totalquantity of iron and silicon not exceeding 0.8% and the amount of ironnot exceeding $4; of the silicon content, and the balance aluminumexcept for other impurities than those named hereinbefore, said cablesheath being characterized by having undergone recrystallization at alower temperature than aluminum containing only impurities including notless than 0.01% each of iron and silicon and not more than a total of0.8% of iron and silicon, but the ratio of said iron to siliconexceeding 4 to 3, where said aluminum has received the same amount ofcold work as said aluminum base alloy cable sheath.

7. An annealed aluminum base alloy cable sheath which prior to annealingreceived at least cold work, said alloy consisting of 0.01 to 0.1%beryllium, 0.15 to 0.5% nickel, a maximum of 0.05 each of copper andmagnesium impurities, at least 0.01% each of iron and silicon, the totalquantity of iron and silicon not exceeding 0.5% and the amount of ironnot exceeding of the silicon content, and the balance aluminum exceptfor other impurities than those named hereinbefore, said cable sheathbeing characterized by having undergone recrystallization at a lowertemperature than aluminum containing only impurities including not lessthan 0.01% each of iron and silicon and not more than a total of 0.5%iron and silicon, but the ratio of said iron to silicon exceeding 3 to4, where said aluminum has received the same amount of cold work as saidaluminum base alloy cable sheath.

References Cited in the file of this patent UNITED STATES PATENTS1,716,943 Archer et a1 June 11, 1929 2,565,768 Gittings Aug. 28, 19512,670,309 McClintock Feb. 23, 1954 OTHER REFERENCES Phillips: TheGrain-size of Rolled Aluminum, The Journal of The Institute of Metals,vol. 68, 1942, pages 47-108, particularly pages 83, 89 and 104.

Spillett: The Structure of Rolled and Annealed Aluminum as Revealed byX-Rays, The Journal of the Inst. of Metals, vol. 69, 1943, pages149-175, particularly pages 149 and -163.

Transactions of The American Society for Metals (1949), vol 41, pages443-459.

Varley: The Recovery and Recrystallization of Rolled Aluminum ofCommercial Purity, The Journal of The Inst. of Metals, vol. 75,1948-1949, pages -202, particularly pages 186, 194.

Mechanical Properties of Metals and Alloys, Bureau of Standards CircularNo. C447 (1943), page 27.

1. AN ALUMINUM BASE ALLOY ARTICLE WHICH HAS RECEIVED AT LEAST 20% COLDWORK, SAID ALLOY CONSISTING OF 0.005 TO 0.25% BERYLLIUM, 0.04 TO 1.0%NICKEL, A MAXIMUM OF 0.05% EACH OF COPPER AND MAGNESIUM IMPURITIES, ATLEAST 0.01% EACH OF IRON AND SILICON, THE TOTAL QUANTITY OF IRON ANDSILICON NOT EXCEEDING 0.5% AND THE AMOUNT OF IRON NOT EXCEEDING 4/3 OFTHE SILICON CONTENT, AND THE BALANCE ALUMINUM EXCEPT FOR OTHERIMPURITIES THAN THOSE NAMED HEREINBEFORE, SAID COLD WORKED ALLOY ARTICLEBEING CHARACTERIZED BY A LOWER TEMPERATURE OF RECRYSTALLIZATION WHENANNEALED THAN ALUMINUM CONTAINING ONLY IMPURITIES INCLUDING NOT LESSTHAN 0.01% EACH OF IRON AND SILICON AND NOT MORE THAN A TOTAL OF 0.8% OFIRON AND SILISILICON, BUT THE RATIO OF SAID IRON TO SILICON EXCEEDING 4TO 3, WHERE SAID ALUMINUM HAS RECIEVED THE SAME AMOUNT OF COLD WORK ASSAID COLD WORKED ARTICLE.